Catalytic conversion of lignocellulosic biomass into industrial biochemicals

ABSTRACT

This invention relates to a method for the conversion of lignocellulosic biomass into ethyl esters of carboxylic acids. Said method consists of treating the biomass material with an oxidizing agent that is incorporated in an solution comprising one or more acids, one or more alcohols and water, and subsequently performing a catalytic reaction at a higher temperature using the same acidic solution into which a larger volume of alcohol is added, in such a way that the catalytic conversion occurs in a medium with a much higher concentration of alcohol, i.e. with a much higher alcohol-to-water wt ratio. Such a method results in relatively high yields of ethyl esters, such as ethyl esters of formic, acetic, and levulinic acids, while producing a low yield of dialkyl ethers, which are unwanted by-products. The concentration of the oxidizing agent in the pre-treatment step is preferably higher than 6.0 wt %. The oxidizing agent is preferably a Fenton or Fenton-type reagent, and most preferably hydrogen peroxide activated by Fe (II), and/or Ti (IV) ions. The alcohol is preferably ethanol, and when ethanol is used, diethyl ether is formed as the unwanted dialkyl ether by-product. Preferably, the biomass material is pelleted before treatment.

FIELD OF THE INVENTION

This invention relates to a method for the conversion of lignocellulosicbiomass into valuable species such as ethyl esters of carboxylic acids.

BACKGROUND

Lignocellulosic materials include materials such as wood, wood wastes,forestry residues, paper-making or cardboard-making residues,agricultural residues, municipal waste, and perennial grasses. Thesematerials mainly contain cellulose, hemicellulose, and lignin in variousproportions.

There are known ways of converting lignocellulosic biomass materialsinto fuels and chemicals. In the case of wood and wood residues, it isknown to convert such materials by first subjecting these to a chemicalpre-treatment to disrupt the protective and chemically recalcitrantlignin layer. This allows access to cellulose and hemicellulose layersby chemical or enzymatic species being incorporated in a subsequenthydrolysis step. Thus, sugars (mainly glucose) can be extracted toproduce, for example, bioethanol by enzymatic fermentation.

It is also known to use harsher conditions, such as stronger acids, foracid hydrolysis of cellulose and hemicellulose of lignocellulosicbiomass. This results in the formation of carboxylic acids such asformic acid, levulinic acid, acetic acid, and furfural. Such chemicaldegradation is industrially exploited in the Biofine process [Reference1].

Production of Alkyl Levulinates and Other Alkyl Esters:

Catalytic conversion of cellulose and hemicellulose into alkyllevulinates and light alkyl esters is currently known to be carried outin a) a single step process or b) a two-step process [Reference 2].

In a typical single step process, alcohol is used as a reactant andsolvent. At least one acidic catalyst is used, typically a mineral aciddiluted in alcohol. The liquid products of the reaction consist of alkyllevulinate, alkyl formate, alkyl acetate, and 2-furfural(2-furfuraldehyde). The use of alcohol allows the occurrence of twochemical reactions: alcoholysis and esterification. However, theby-product dialkyl ether is also produced directly from the alcohol insignificant amounts, said amounts varying with the process conditionssuch as temperature and exposure time. If the alcohol is ethanol, thisether is diethyl ether (ethyl ether). Diethyl ether, because of its highvolatility at room temperature, is generally considered as aninconvenience in various process operations (such as handling andstorage), and because of its low commercial value and limited marketdemand. Solid residues (commonly called lignin char) are also producedin significant quantities.

In a typical two-step process, both catalytic steps involve acidcatalysts. The first step is the hydrolysis of cellulose andhemicellulose: this catalytic reaction uses water as a solvent, andproduces levulinic acid as well as by-products such as formic acid,acetic acid, and 2-furfural. Most of the water is subsequently withdrawnfrom the reaction medium and replaced with ethanol [Reference 2]. Thus,esterification (of the resulting carboxylic acids) occurs in the secondstep, producing alkyl esters. Under some harsh conditions, 2-furfuralresulting from the acid catalyzed degradation of the reactionintermediates of hemicellulose is partially converted into formic acid.

In a previous patent application entitled “Catalytic conversion oflignocellulosic biomass into fuels and chemicals” [Reference 3] and a2012 publication in Catalysis Letters [Reference 4], preference wasgiven to a single step process. In that invention, two novelties wereintroduced to the conventional approach:

-   -   a) The liquid product (esters) yields were significantly        increased by having a Fenton reagent directly incorporated into        the acidic ethanol solution. It is to note that the Fenton        reagent comprised an oxidant (hydrogen peroxide, H₂O₂), coupled        with Fe (II) and/or Ti (IV) ions [References 2, 3]. The        incorporation of a Fenton reagent in the conventional acid        catalyzed hydrolysis/ethanolysis of cellulose and hemicellulose        did not significantly change the products spectrum, i.e. the        same esters and oxygenates were produced, although in higher        yields. In addition, some methanol was produced when Fenton        reagents were used.    -   b) The unwanted diethyl ether was removed from the product        liquids and then sent over a ZSM-5 based catalyst for its        conversion into hydrocarbons [References 3, 4].

In that invention, the incorporation of the Fenton reagent in theconversion medium resulted in a rapid and important size reduction ofthe biomass materials, such a phenomenon being accompanied by a sudden,albeit limited, rise in temperature and pressure. This was indicative ofsome destructive action due to the free radicals generated by the Fentonreagent.

The total product yield of the process increased with increasing amountof Fenton reagent, particularly with increasing the proportion ofhydrogen peroxide. However, due to its relatively high cost, theincrease in hydrogen peroxide consumption results in higher productioncosts.

It is also known from WO 2014/144588 to treat biomass in other toincrease the porosity of cellulosic material, remove lignin fortreatment into sugars followed by optional acid hydrolysis. Apre-treatment using ionic liquids is used to swell the biomass prior toan second step alkaline treatment to release the lignin and a third stepor acid or enzymatic hydrolysis. The ionic liquids are selected fromcation structures that include imidazolium, pyrrolidinium, pyridinium,phosphonium, ammonium, or functionalized analogs thereof [Reference 5].

Finally, it is also know from CA 2872510 to pre-treat biomass bymechanical breakdown which does not substantially affect the lignin,cellulose and hemicellulose compositions of the biomass. Acid extractionis used to generate a sugar stream which is then treated with an amineextractant to remove impurities. [Reference 6].

Therefore, there is a need for an improved method that allows for theconversion of lignocellulosic biomass into ethyl esters of carboxylicacids, wherein the production of the DEE by-product is minimized; andwherein there is a decrease in the consumption of oxidizing agent.

SUMMARY OF THE INVENTION

This invention relates to a method for the conversion of lignocellulosicbiomass into ethyl esters of carboxylic acids. Said method consists offirst treating the biomass material with an oxidizing agent in an acidicsolution of alcohol and water, and subsequently performing a catalyticreaction at a higher temperature using the same acidic solution intowhich a large volume of alcohol is added. Accordingly, the catalyticconversion occurs at a much higher concentration of alcohol, i.e. with amuch higher alcohol-to-water wt ratio.

The invention thus provides the following according to aspects thereof:

A method for converting lignocellulosic biomass materials into ethylesters, said method comprising the following steps:

-   -   a) thermo-chemical pre-treatment of the biomass materials with        an oxidizing agent solubilized in an acidic solution comprising        an acid, an alcohol, and water, thereby forming a pre-treatment        slurry;    -   b) diluting the slurry with additional alcohol and optionally        additional acid species, such as sulfuric acid, obtaining        catalytic conversion of the biomass materials in the slurry into        ethyl esters; and    -   c) recovery of the resulting products, wherein the resulting        products include the ethyl esters.

Other objects, advantages and features of the present invention willbecome more apparent upon reading of the following non-restrictivedescription of specific embodiments thereof, given by way of examplewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 shows the general conversion method of an embodiment of thepresent invention.

FIG. 2 shows the variation of the total product yield CP (in wt %, withthe exclusion of the diethyl ether, DEE, yield) as a function of theconcentration of oxidant (H₂O₂) in a Fenton reagent (HP, expressed in wt% of the catalytic conversion solution), in accordance with an exampleof a method known in the prior art.

DETAILED DESCRIPTION OF THE INVENTION

To provide a clear and consistent understanding of the terms used in thepresent specification, a number of definitions are provided below.Moreover, unless defined otherwise, all technical and scientific termsas used herein have the same meaning as commonly understood to one ofordinary skill in the art to which this disclosure pertains.

The use of the word “a”, “an” or “the” when used in conjunction with theterm “comprising” in the claims and/or the specification may mean “one”,but it is also consistent with the meaning of “one or more”, “at leastone”, and “one or more than one”.

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “include” and “includes”) or “containing”(and any form of containing, such as “contain” and “contains”), areinclusive or open-ended and do not exclude additional, un-recitedelements or process steps.

As used herein the term “about” is used to indicate that a valueincludes an inherent variation of error for the device or the methodbeing employed to determine the value. In the present application,reference to numerical values are understood to be approximate or aboutthat value owing to normal variations in methodology or measurements.Unless otherwise indicated, the term “about” will allow plus or minusvariations of 10%. Unless otherwise indicated the reporting of numericalvalue are understood to be approximate regardless of the use of the word“about” in relation to the numerical value.

The data of FIG. 2 and the observed phenomena as reported above, withrespect to the single-step process discussed in [Reference 3]and[Reference 4]suggests that the disruptive action of the free radicals(being generated by an oxidizing agent, preferably a Fenton or aFenton-type reagent) on the lignin layer of the biomass material, occursin the liquid phase. Moreover, for such solution to be efficient, itsoxidizing agent concentration, preferably H₂O₂ concentration, ispreferably higher than 6 wt %.

The present invention incorporates into the process a pre-treatment stepaimed at degrading the biomass structure. Essentially, this step iscarried out with a liquid solution having a much smaller volume thanthat used in the prior art. However, the related volume is preferablysufficient to keep the biomass material totally immersed into thatliquid. As a result, it is possible to maintain an oxidizing agentconcentration, preferably a H₂O₂ concentration, higher than about 6 wt %while considerably reducing the amount of the oxidizer used. The presentinvention also supposes that the oxidizing agent, preferably H₂O₂, doesnot need to intervene in the subsequent step of“hydrolysis-esterification” (catalytic conversion), which requires alarger liquid volume and a higher reaction temperature.

In one embodiment of the present invention, the method comprises thefollowing steps:

-   -   a) Biomass pre-treatment: is carried out by submitting the        biomass material to a combined effect consisting of the        degradation of the biomass structure by an oxidizing agent,        preferably a Fenton reagent, and by an acidic species. A minimal        amount of liquid should be used in order to have a concentration        of oxidizing agent higher than about 6 wt % while having the        biomass material essentially all immersed in the liquid.        However, in this phase, neither water nor alcohol can be used        alone because the next step of the method includes several        catalytic reactions (biomass hydrolysis/esterification), thereby        requiring water and alcohol, preferably ethanol, in well-defined        proportions. Thus, the pre-treatment phase is done in an acidic        solution of alcohol, preferably ethanol, and water, and in the        presence of an oxidizing agent, preferably a Fenton reagent: all        these components are preferably incorporated into the reaction        medium with precise timing. The maximum temperature used is        preferably about 150° C., which is also the boiling point of        hydrogen peroxide.    -   b) Final biomass conversion: this step is performed over the        resulting degraded biomass at a higher temperature, preferably        at around 180° C., upon addition of alcohol, preferably ethanol,        and adjustment of the acidity. In such a context, water is used        as a dialkyl ether inhibitor, preferably a DEE inhibitor if        ethanol was used. However, the amount of water is preferably        regulated because if there is too much water in the reaction        medium, it may negatively affect the total product yield.        Finally, some polymerization inhibitor can be added in order to        prevent an excessive formation of polymeric species that may        contribute to some decrease in the final product yields.

FIG. 1 shows the general conversion scheme of a specific embodiment ofthe present invention, illustrating controlled use of Fenton orFenton-type reagents during a biomass pre-treatment phase, thus allowinga subsequent catalytic reaction to produce ethyl esters in relativelyhigh yields. It also illustrates the use of acidic solutions of alcoholand water in both pre-treatment and conversion phases, which candrastically reduce the formation of dialkyl ethers, an unwantedby-product.

The method of the present invention results in relatively high yields ofethyl esters, preferably ethyl esters of formic, acetic, and levulinicacids, while producing a low yield of dialkyl ethers, unwantedby-products. Thus, the method of the present invention shows twoimportant practical advantages when compared to that of the prior artthat also made use of oxidizing agents: a) there is a reduction inunwanted by-products with basically no or little need of up-grading theunwanted dialkyl ethers; and b) the process consumption of oxidizingagent is greatly reduced.

According to one embodiment of the present invention, the concentrationof the oxidizing agent used in the biomass pre-treatment phase ispreferably above about 6.0 wt %.

In a further embodiment of the present invention, the use of apolymerization inhibitor in step b) is preferred.

In yet another embodiment of the present invention, the method resultsin relatively high yields of ethyl esters of formic, acetic, andlevulinic acids, and a significant production of levulinic acid,furfural, methanol, α-angelica-lactone, methyl levulinate and dialkylsuccinate.

In an additional embodiment of the present invention, the“water-to-alcohol” weight ratio in the reaction medium has someinfluence on the products' “levulinic acid-to-ethyl levulinate” weightratio. Interestingly, it is possible to limit the production of dialkylethers to an acceptable level by adjusting the reaction parameters,particularly by adjusting the “water-to-alcohol” weight ratio in themain conversion step.

In another embodiment of the present invention, it is possible tofurther reduce the volume of the liquid phase used in the pre-treatmentstep, while maintaining a sufficiently high oxidizing agentconcentration, preferably H₂O₂ concentration, by increasing the bulkdensity of the biomass material prior to submitting it to thepre-treatment operation. In fact, “pelleting” or “pelletizing” thesematerials can significantly increase their specific density. This inturn allows to use less liquid to achieve immersion of a given volume ofbiomass material. Such a densification of biomass materials can becarried out with a binder (rice-husk pellets) or without a binder (woodpellets). In addition to an advantageous reduction of the consumption ofthe oxidizing agent, this pelleting can reduce the overall volume ofother reagents (including acid species) and solvents used in theprocess.

The invention is illustrated in further detail by the followingnon-limiting examples.

Examples 0-5 (Comparative)

In prior art methods using a Fenton reagent, wherein said Fenton reagentis directly added to the reaction medium to enhance the production ofalkyl esters [References 3, 4], high concentrations of the oxidant(hydrogen peroxide) in the conversion solution were needed to achievehigh yields of alkyl esters. Otherwise, in the absence of the Fentonreagent, such yields were quite low. FIG. 2 and Table 1 report theresults obtained with these known methods.

FIG. 2 shows the variation of the total product yield CP (in wt %, withthe exclusion of the diethyl ether, DEE, yield) as a function of theconcentration of the oxidant (H₂O₂) in the Fenton reagent (HP, expressedin wt % of the conversion solution), in accordance with an example of aprior art method.

The corresponding values of HP and CP, as well as B/HP(biomass-to-hydrogen peroxide wt ratio) are reported in Table 1:

TABLE 1 Total product yield versus H₂O₂ concentration HP Example number0 1 2 3 4 5 HP (H₂O₂) 0 5.7 7.3 8.1 9.3 11.6 B/HP — 3.6 2.8 2.6 2.2 1.8CP 37 38 60 85 97 103 Note: (there is no pre-treatment step in the priorart method)

Thus, HP has an important influence on the total product yield (CP).

FIG. 2 shows that the total product yield starts steadily increasingwhen the value of HP is higher than about 6.0, corresponding to a valueof B/HP lower than about 3.3 (Table 2). The latter parameter indicatesthat at least 30 g of hydrogen peroxide are needed for obtaining a totalproduct yield CP higher than 38 wt % (conventional value reported whenFenton reagents are not in use).

Table 2 shows some typical results obtained with the prior art method:

TABLE 2 Typical performances of the catalytic conversion of sprucechips, in accordance with the method of the previous invention Examplenumber 0 2 4 HP 0 7.3 9.3 B/HP — 2.8 2.2 H₂O₂ consumed in g 0 36 45.5per 100 g of dried biomass) Product yield (wt %) Ethyl formate 5 17 37Ethyl acetate 4 14 24 Ethyl levulinate 18 20 22 Methanol 0 3 52-furfural (and other 1 5 9 oxygenates) CP 28 59 97 Diethyl ether (DEE)64 52 60

Thus, in accordance with the prior art, higher product yields(particularly for short esters, i.e. ethyl formate and ethyl acetate)are obtained with higher concentrations of hydrogen peroxide HP, leadingto higher total product yield CP (excluding DEE). Unfortunately, theyield of DEE is also very high.

Typical Procedure Used for the Biomass Catalytic Conversion of thePrevious Invention (Example 4 of Table 1 and Table 2):

45.0 g of spruce wood chips (dried in an oven at 80° C. for 48 hours),were added to solution A, being contained in a Parr reactor (capacity=1liter) and made from 132 g of absolute ethanol and 41 g of aqueoushydrogen peroxide (50% H₂O₂), equivalent to 45.5 g of H₂O₂ per 100 g ofdried biomass. Then, solution B, 2.0 g of ferrous sulphate heptahydratedissolved in 24 g H₂SO₄ (17 wt %) and 17 g water, was slowly added undercooling and mild stirring.

Composition: liquid=215 g; liquid/biomass=4.8; H₂O₂ (HP)=9.3 wt %;acidity=1.9 wt %; ethanol/water=4.1; biomass/H₂O₂ (B/HP)=2.25 (meaningthat for treating 100 g of biomass, 44 g of H₂O₂ were necessary).

Then, the autoclave was heated to the reaction temperature of 181° C.and maintained at said temperature for 60 min.

In the prior art method, due to high yields of the by-product diethylether (DEE), as reported in Table 2, the method needed a secondcatalytic step (conversion over a zeolite based catalyst) to convert theimportant amounts of DEE (DEE up-grading). In addition, the largeconsumption of hydrogen peroxide, which is quite expensive and notreadily available, may significantly affect the production costs ofvaluable biochemicals, particularly that of ethyl levulinate.

Examples 6 (Comparative) and Examples 7-10

Data obtained using an embodiment of the method of the present inventionare reported in Table 3 as Examples 7-8.

TABLE 3 Conversion of spruce chips using an embodiment of the presentinvention Example number 6 7 8 HP _((*)) NO 6.6 6.6 B/HP — 5.6 5.6Polymerization inhibitor NO NO YES Product yield (wt %) Ethyl formate 713 14 Ethyl acetate 5 9 10 Ethyl levulinate 14 21 22 Levulinic acid 1 32 Furfural 3 1 1 Methanol 0 3 4 Diethyl succinate & other 2 3 3oxygenates DEE 6 7 7 CP (excluding DEE) 32 54 56 Note: HP _((*)) =concentration of H₂O₂ in the pre-treatment liquid phase, expressed as %wt.

In preferred embodiments of the present invention as illustrated byexamples 7 to 10, the following procedure is provided for:

-   -   I) Pre-treatment step:        -   A given mass of biomass material is soaked with Solution A,            wherein Solution        -   A contains ethanol, sulfuric acid diluted in ethanol, and            hydrogen peroxide.        -   Afterwards, Solution B, containing ferrous sulfate dissolved            in water, is rapidly added under cooling to form a slurry,            so that the following conditions are satisfied:        -   a) Liquid/biomass wt ratio=1.5-3.        -   b) Hydrogen peroxide concentration=above 6.0 wt %.        -   c) Acidity=2.0-4.0 wt %.        -   d) The slurry is heated in an autoclave at a temperature            between 85° C. to 145° C. for 1 to 5 hours.    -   II) Catalytic conversion step:        -   Solution C, containing sodium sulfite dissolved in water,            and solution D, containing ethanol and eventually some            sulfuric acid diluted in ethanol, are successively added.

In step II), the reaction conditions are as follows:

-   -   a) Liquid/biomass wt ratio=3.5-7.0    -   b) Acidity=1.2-2.3 wt %.    -   c) Ethanol/water wt ratio=3.5-5.5    -   d) Reaction temperature=170° C.-190° C.    -   e) Reaction time=25 min-120 min.

Table 3 shows that:

-   -   a) The use of an oxidizing agent, preferably a Fenton or        Fenton-type reagent, in the pre-treatment step, leads to higher        yields of all ester products (Examples 7 and 8, versus Example        6), and to an increased production of methanol.    -   b) Water in significant concentration in the conversion medium        results in the production of valuable levulinic acid (for        comparison, in all examples of Table 2, there is almost no        levulinic acid produced), and is the most likely cause of the        strong decrease in dialkyl ether production, which was DEE in        this embodiment of the present invention (Examples 7 and 8 of        Table 3 versus Examples 2 and 4 of Table 2).    -   c) In Examples 7 and 8 of Table 3, the B/HP (biomass-to-hydrogen        peroxide used) ratio has a value of 5.6, which is much higher        than those reported in Examples 2 and 4 of Table 2 (prior art).        This is because the amount of H₂O₂ added into the pre-treatment        step is much smaller than the amount added to the conversion        medium of the prior art (a process having no pre-treatment        step). Here, a B/HP of 5.6 means that for treating 100 g of        dried spruce chips, only 18 g of hydrogen peroxide are needed,        as opposed to the 36 g of oxidizer (B/HP=2.8) used in Example 2        of Table 2, despite both examples having almost the same total        product yield CP.    -   d) The use of a polymerization inhibitor (sodium sulfite in        Example 8 of Table 3) significantly increases the total product        yield (Example 7 of Table 3). Another inhibitor that can be used        is magnesium sulfite trihydrate.

Preferred Embodiment of Example 8 (Table 3)

a) Pre-Treatment Step:

50.0 g of spruce wood chips, dried in an oven at 80° C. for 48 hours,were added to solution A, being contained in a Parr reactor (capacity=1liter) and made from 40 g of H₂SO₄ dissolved in absolute ethanol (10 wt%), 56 g of absolute ethanol, and 18 g of aqueous hydrogen peroxide (50%H₂O₂). Then, solution B (1.1 g of ferrous sulphate heptahydratedissolved in 22 g water) was slowly added under cooling and mildstirring to form a slurry.

Composition: total liquid=137.1 g; liquid/biomass=2.7; acidity=2.9 wt %,hydrogen peroxide=6.6 wt %; ethanol/water=2.3.

The slurry is then heated very slowly to 140° C. The temperature is heldat that value for 2 hours.

b) Catalytic Conversion Step:

Solution C (1.4 g of sodium sulfite dissolved in 6 g of water) andsolution D (12 g of H₂SO₄ dissolved in absolute ethanol (10 wt %)+97 gof absolute ethanol) were successively added.

Composition: liquid=254 g; liquid/biomass=5.1; acidity=2.0 wt %;ethanol/water=4.3.

The resulting solution is heated to 179° C. and that temperature is keptconstant for 60 minutes.

The amount of oxidizing agent, advantageously hydrogen peroxide, used inthe pre-treatment phase plays a role in the method of the invention.Table 4 shows the effect of the biomass-to-hydrogen peroxide wt ratio(B/HP) on the product yields. It is important to note that in allexamples of Table 4, all reaction parameters are the same (see preferredembodiment of Example 8 of Table 3), except for the amount of hydrogenperoxide used in the pre-treatment phase, in that there is variation inthe amount of hydrogen peroxide adjusted with water used in examples 9and 10.

TABLE 4 Influence of the HP (*) and B/HP ratio on the product yields.Example number 9 8(**) 10 HP (*) 7.3 6.6 5.8 (B/HP) 5.0 5.6 6.3 H₂O₂consumed/100 g dried 20 18 16 Biomass Product yield (wt %) Ethyl formate15 14 13 Ethyl acetate 12 10 9 Ethyl levulinate 23 22 21 Levulinic acid3 2 2 Furfural 1 1 1 Methanol 4 4 3 Diethyl succinate & others 2 3 2 DEE13 7 8 CP (excluding DEE) 60 56 51 HP (*) = concentration of H₂O₂ in thepre-treatment liquid phase expressed as % wt; (**)same as Example 8 ofTable 3;

When directly comparing Example 2 of Tables 1 and 2 (using the method ofthe prior art, References 3 and 4), and Example 8 of Tables 3 and 4(using an embodiment of the method of the present invention), thefollowing conclusions can be reached:

-   -   a) Both runs provide similar total product yields CP (excluding        DEE).    -   b) The production of DEE with this embodiment of the method of        the present invention is minimal in comparison to the prior art.    -   c) The consumption of hydrogen peroxide per 100 g of dried        biomass with the method of the present invention is only about        half of that of the prior art (18 g versus 36 g).

Thus, by using the method of the invention instead of that of the priorart, it is possible to very significantly decrease the amount ofhydrogen peroxide used while obtaining almost the same yield ofcommercially valuable products, in particular ethyl levulinate.

In addition, the method of the invention when compared to that of theprior art, significantly decreases the amount of the “unwanted” DEE. Itis to note that DEE is produced directly from ethanol by dehydration.Thus, “less DEE produced” means “lower ethanol consumption”.

Significantly lower consumption of fed hydrogen peroxide andsignificantly lower consumption of fed ethanol mean lower productioncost for the product esters.

The invention of a specific pre-treatment phase that uses a reducedliquid volume (with respect of the total volume of the main catalyticconversion phase) in conjunction with a sufficient concentration ofhydrogen peroxide, allows further improvement of the process (by“densification” of the biomass feed). In fact, by reducing the size ofthe biomass chips, it is possible to increase the B/HP ratio (morebiomass material converted for the same mass of hydrogen peroxide used).

An advantageous finding according to embodiments of the presentinvention was also noted: the final products obtained from the catalyticconversion step do no vary as a function of the impurities present inthe initial biomass charge.

It is to note that there is no reaction with the Fenton Reagent when thetemperature is equal or lower than 40° C. However, when the reactionvessel is heated at a temperature higher than 45° C., there is aspontaneous and quite rapid increase of temperature (to 105-110° C.,generally at a rate of 20° C./min) and pressure (40-45 psi) that mayhelp disrupting the ligno-cellulosic structure of the biomass.

The method of the invention, when used with a biomass conversion mediumcontaining only water (used as a solvent as in a conventional acidhydrolysis) leads to the same level of yield increase (mostly forlevulinic acid). Therefore, this beneficial effect can be attributed tothe action of the oxidizing agent, which in this embodiment of thepresent invention was a Fenton reagent.

Ethyl levulinate and its carboxylic acid, levulinic acid, have numerouscommercial applications [2]. These compounds are considered as platformchemicals, meaning that they can lead to the production of numerousother industrial chemicals [2].

It is important to note that all ethyl esters obtained by the method ofthis invention (particularly ethyl formate and ethyl levulinate) can beconverted into their corresponding carboxylic acids via knownacid-catalysed hydrolysis. To do so, solid acidic catalysts such aszeolites and special acidic ion-exchange resins are preferred owing tosome advantages associated with their use.

It is also important to note that diethyl ether DEE can be converted, ifnecessary, to other chemicals such as light olefins or ethyl acetate, orconverted back to ethanol.

DEE can be converted to light olefins and heavier hydrocarbons(particularly, aromatics), over zeolite catalysts, particularly ZSM-5zeolite (Si/Al ratio=from 40 to 60), at a temperature ranging from 280°C. to 320° C., and a W.H.S.V. (weight hourly space velocity), rangingfrom 1.0 h⁻¹ to 4.0 h⁻¹. It is advantageous to dilute DEE with water inthe proportion (water/DEE) of 1/2 to 2/1 in order to reduce the rate ofcarbonaceous deposition onto the zeolite acid sites, minimizing thus thecatalyst fouling. The latter phenomenon, if being important, needs a toofrequent catalyst regeneration by combustion in air at elevatedtemperatures (450-550° C.). Total hydrocarbon yield can exceed 90 wt %in most preferred operating conditions.

DEE can also be converted into ethyl acetate with acetic acid over anacidic catalyst. Solid acidic catalysts are preferred for easyproducts/catalyst separation reason. The most preferred solid acidiccatalyst is the H-USY (acid form-ultra stabilized Y zeolite) for itsstructural robustness and its relatively high yield of ethyl acetate(more than 60 wt % at 300° C.).

DEE can also be converted back to ethanol with water over an acidiccatalyst at high temperature and high pressure.

The method of this invention has characteristics for successfulcommercial development, i.e. simple, green, and sustainable technology,with low cost production of valuable chemicals used in various fields ofchemical industry.

The scope of the claims should not be limited by the preferredembodiments set forth in the examples, but should be given the broadestinterpretation consistent with the description as a whole.

The present description refers to a number of documents, the content ofwhich is herein incorporated by reference in their entirety.

REFERENCES

-   [1] D J. Hayes, S. Fitzpatrick, M. H. B. Hayes, J. R, H. Ross, in    Biorefineries-Industrial Processes and Products, Wiley-VCH (2006) p.    139-164.-   [2] R. Le Van Mao, Q. Zhao, G. Dima, D. Petraccone, Catal.    Lett, (2011) 141, 271-276; and refs. therein.-   [3] R. Le Van Mao, WO 2013/127006 A1.-   [4] R. Le Van Mao, A. Muntasar, D. Petraccone, H. T. Yao, Catal.    Lett. (2012) 142, 667-675; and refs. therein.-   [5] WO 2014/144588, Suganit Systems Inc.-   [6] CA 2872510, Virdia Inc.

The invention claimed is:
 1. A method for converting lignocellulosicbiomass materials into ethyl esters in a reaction vessel, said methodcomprising: (a) pre-treatment of the biomass materials with an oxidizingagent solubilized in an acidic solution comprising an acid, ethanol, andwater, thereby forming a pre-treatment slurry; (b) diluting the slurrywith additional ethanol and optionally additional acid species; (c)heating the slurry to a temperature of 170-190° C. and adding apolymerization inhibitor thereby obtaining catalytic conversion of thebiomass materials in the slurry into ethyl esters; and (d) recoveringthe resulting products, wherein the resulting products include the ethylesters.
 2. The method of claim 1, wherein the ethyl esters are selectedfrom the group consisting of: ethyl levulinate, ethyl formate, ethylacetate, and combinations thereof.
 3. The method of claim 1, wherein theoxidizing agent is hydrogen peroxide.
 4. The method of claim 1, whereinthe oxidizing agent is a Fenton.
 5. The method of claim 1, wherein theFenton reagent is hydrogen peroxide activated b at least one of Fe (II)ions or Ti (IV) ions.
 6. The method of claim 1, wherein theconcentration oxidizing agent in the acidic solution used in thepre-treatment step (a) is higher than about 6.0 wt %.
 7. The method ofclaim 1, wherein the solution-to-biomass wt ratio in the pre-treatmentstep (a) is between about 1.0 to about 5.0.
 8. The method of claim 7,wherein the solution-to-biomass wt ratio in the pre-treatment step (a)is between about 2.0 and about 2.7.
 9. The method of claim 1, whereinthe ethanol-to-water wt ratio in the pre-treatment step (a) is betweenabout 0.5 and about 4.0.
 10. The method of chum 9, wherein theethanol-to-water wt ratio in the pre-treatment step (a) is between about1.5 and about 2.2.
 11. The method of claim 1, wherein the acid or theoptionally additional acid species is sulfuric acid.
 12. The method ofclaim 1, wherein the slurry prepared during the pre-treatment step (a)is heated at a temperature between about 65° C. and about 145° C. 13.The method of claim 12, wherein the slurry prepared during thepre-treatment step (a) is heated at a temperature between about 120° C.and about 135° C.
 14. The method of claim 1, wherein the slurry isheated for 1 hour to 6 hours during the pre-treatment step (a).
 15. Themethod of claim 14, wherein the slurry is heated for 2 hours to 4 hoursduring the pre treatment step (a).
 16. The method of claim 11, whereinthe concentration of sulfuric acid during the pre-treatment step (a) isbetween about 1.5 and about 4.0 wt %.
 17. The method of claim 16,wherein the concentration of sulfuric acid during the pre-treatment step(a) is between 2.5 and 3.5 wt %.
 18. The method of claim 11, wherein theconcentration of sulfuric acid in the catalytic conversion step isbetween 1.2 wt % and 2.3 wt %.
 19. The method of claim 1, wherein theconcentrations of biomass material, acid, oxidizing agent, ethanol, andwater are adjusted before or during the operation using the samereaction vessel.
 20. The method of claim 19, wherein the concentrationsof biomass material, acid, oxidizing agent, ethanol, water, andpolymerization inhibitor are adjusted before or during the operationusing the same reaction vessel.
 21. The method of claim 1, wherein thepolymerization inhibitor selected from the group consisting of magnesiumsulfite trihydrate, sodium sulfite, or any combination thereof.
 22. Themethod of claim 1, wherein the resulting products selected from thegroup consisting of ethyl levulinate, ethyl formate, ethyl acetate,levulinic acid, furfural, methanol, α-angelica lactone, methyllevulinate, diethyl succinate, and any combination thereof.
 23. Themethod of claim 1, further comprising the additional step of increasingthe bulk density of the biomass materials prior to submitting saidbiomass materials to the pre-treatment step (a).
 24. The method of claim23, wherein the step of increasing the bulk density of the biomassmaterials comprises pelleting the biomass materials.
 25. The method ofclaim 1, further comprising the additional step of hydrolyzing the ethylesters into their corresponding carboxylic acids.
 26. The method ofclaim 1, wherein the ethanol-to-water wt ratio in the pre-treatment step(a) is between about 1.0 and about 3.3.
 27. The method of claim 1,wherein the solution-to-biomass wt ratio in the pre-treatment step (a)is between about 1.5 and about 4.0.